Fluorescent tube lighting system and apparatus



J. H. BRIDGES Sept. 23, 1952 FLUORESCENT TUBE LIGHTING SYSTEM ANDAPPARATUS Filed Aug. 20. 1948 INVENTOR.

JOHN HEROLD Bmoszs H\5 ATTORNEY Patented Sept. 23, 1952 UNITED STATESPATENT OFFICE "FIJUORESCENT TUBE LIGHTING SYSTEM AND APPARATUS 361mHerold Bridges, Atlanta, Ga, 'as s'ignor ft'o National 'InventionsCorporation, .a corporation of New Jersey Application August 20,1948,Serial'No. 45,357 5 Claims. (01. 315-455) My invention relates generallyto electrical lighting systems and'applicationsand more;particularlyconcerns a fluorescent tube lighting system and the several partscomprisin thesame. An object of my invention is to provide a fluorescenttub lighting system which is simple and inexpensive of production; whichis highly efficient, economical and certain in operation, at the sametime insuring 'instantstarting .of the tubes, and subsequent maintenancethereof, in certain manner under even the most adverse weatherconditions; and which has a high system power-factor with lowstroboscopic effect, and in which the tube currents are effectivelycontrolled.

Another object is to provide axpower unit fora fluorescent tubelightingtsystem which is unitary and compact, involving a minimumofspace requirements; which is comprised ofcor'nponent parts which arein themselvessimple and economical of production; and which is; sturdyand reliable in operation,"having'long useful life and involving aminimumiron'and coppercontent, at the same time giving rise :to highlyefficient, reliable and economical system operation.

Yet another objectis to provide at-transformer and associatedironcorezchoke coil for use in a fluorescent tube lighting system *where.initial cost are to beat a minimum and where-space requirements are ata premium, but wherereliable and efficient operationisrequired.

Other advantages in part will be obvious and in part more fully pointedout hereinafter during the course of the following description.

Accordingly, my invention resides in :the several parts, elements and"features of construction, as well as in the combination of each of thesame with one or more of the others, the-scope cfthe application of allof which will be more fully set forth in the claims at'the end of thisspeification. I

Throughout the several views of "the drawings, wherein I have disclosedthat embodiment of my invention which I prefer atpresent, and in whichlike reference characters denote like parts:

Figure 1 is a schematic wiring diagram, disclosing the basic principlesof 'my invention; while Figure 2 is a view, partly inperspective andpartly schematic, disclosing the power unit/according to my invention ainstalled in a practical embodiment.

As conducive to a more thorough understanding of my invention, it maybenoted-at this-point that wide acceptance in the'arts, commerce and 2industry, has been achieved by fluorescent tube lighting systems. Thegrowth has been .so rapid that fluorescent tube lighting is closelyapproachin in incandescent lighting in popularity.

Equipment displaying better and better operating characteristics isproduced, while both production and operating costs-areundergoing.constant reduction.

Savings in the amountrof copperand iron employed are constantly soughtfor. Reduction in the space requirements of the operating units is aconstant objective. Efforts are continuously being made to reduce thecost of the power unit required and yet maintainsatisfactory operatingcharacteristics.

An important object of my invention, therefore, is to provide a-compact,.inexpensiveand efficient-power unit-for operating apairof'fiumrescenttubes with unobjectionable stroboscopic effect, satisfactory powerfactor and instant startin under'the varying conditions of actual use. al

In accordance with'the practice of my invention, I operate pairedfluorescent tubes from a transformer common to both of them.LPIr'efe'rably, although not necessarily, lthis transformer has ashell-type core, and the primary and secondary windings are mounted onthe centrallleg thereof, preferably but not necessarily side-byside, inautotransformer connection.

I Now, to insure good operating characteristics, with highsystempower-factonl connectgthetwo fluorescent tubes in series with eachother and with the transformer. iron core inductive reactance also isincluded in this series circuit, preferably being introduced betweenthesecondvary winding .ofthe transformer and the fiuorescent tube towhich it is connected. lhisseries has ashore to prevent excessivecurrent while the tubes are intheir 'conductiize' condition. I

also connecta condenser across one tubapreferably across the reactanceandJthe tube to which it is immediately connected. This permits initialstriking-of the .un'shunted tube followed by striking of theshuntedftube. ,Thevdltage'requirements of the transformer are only thatof one tube.

In my novel construction, "the close-coupled tran'sfornier is compact'and inexpensive. Moreover, the inductance-likewise iscompact'andinexpensive. 'Addi tionally, "I am enabled to achieve thefurther simplification of fOIh'lillg" the transwarm r secondarywindingand thec'hoke coil winding of the same size wire since a common currentflows -th rough boith, Asubstantialegaving in manufacturing 'c'osts thusis achieved.

For a more precise understanding of my lighting system and apparatus,reference is had more particularly to the schematic embodimentillustrated in Figure 1 of the accompanying drawing wherein thetransformer is indicated generally by the reference number I 0. Itconsists of a shell-type iron core indicated generally at H, having acentral leg HA and outer legs IIB, I IC disposed parallel with and inspaced relation to the central leg II, one on each side thereof. Thecore is completed by end pieces IID and HE. A primary winding I2 and asecondary winding I3 are disposed on the central leg HA. Leads I4, I5extend from the extremities of the primary I2 to a suitable source ofalternating current power, indicated generally at I6.

For reasons which will be developed more particularly hereinafter, theprimary and secondary windings I2 and I3 are disposed side-by-side onthe central leg IIA. That is, they are not disposed in superimposedrelation, one on top of the other. It will be noted that the transformerwindings are close-coupled, the only flux leakage being to the air fromthe margins of the core. Preferably, although not necessarily, theprimary and secondary windings are connected in autotransformerconnection. Such connection is entirely permissible, under theregulations of the Fre Underwriters, for potential of 600 volts or less.Illustratively, the primary may be wound for 118 volts while thesecondary is wound for 332 volts, giving an output potential for theautotransformer of 440 volts.

To achieve a high degree of economy, the winding I2 is constructed ofwire of sufiicient diameter to carry the higher primary current, whilethe winding I3 is formed of wire size just sufficient to carrycontinuously the prevailing secondary current. For two 40 wattfluorescent tubes, this amounts to approximately 0.9 amperes. With thecurrent-carrying capacities of the windings I2 and I3 being accuratelydetermined, and as well, the number of turns of both primary andsecondary windings being nicely selected for inducing the propersecondary voltage, the minimum copper requirement is accuratelydetermined, and is maintained at a very low figure.

The central leg IIA of the transformer core is dimensioned to carry,just short of magnetic saturation, the maximum flux required for inducing the required secondary voltage, while the outer members IIB, IIC,IID and HE are dimensioned as to accommodate, just short of magneticsaturation, about one-half of the maximum flux coursing the central legI IA.

Minimum iron content is determined by maintaining the core length at thesmallest possible value consistent with placing the primary andsecondary windings I2 and I3 in side-by-side relation thereon, and byinsuring that the spacing between outer legs HB and HG, on the one hand,from the central leg I IE on the other hand, is maintained at thesmallest possible value consistent with suppression of mutual inductionbetween the central and outer legs. That is, the pieces IID and HE aremaintained at minimum length. In this manner, and by the observance ofthe several precautions hereinbefore recited, the greatest possibletransformer efiiciency is achieved, both from an operational andpractical, economical standpoint, and both the first costs and the costsof subsequent operation are brought to a theoretical minimum.

From a manufacturing standpoint, the cost is minimized since theelements of the transformer are of the greatest possible simplicity. Tofacilitate simplicity in manufacture, although the following does notnecessarily constitute a material part of my invention, the outer legs IIB and I IC may be formed with integral end pieces I ID and HE giving apair of generally C-shaped core pieces abutting the linear central legHA (see Fig. 2), the several elements being tightly clamped togetheragainst chattering.

Paired fluorescent lamps I8, I9, in the present instance comprisingconventional 40 watt lamps, although this is not an essentialprerequisite, are connected in series with each other through leads 20and 2|, joined together at junction 22. A current-limiting chokeindicated generally at 23 is likewise connected in series with the tubesI8 and I9 by means of a lead 24 between one terminal of tube I8 and acorresponding terminal of choke coil winding 25. The ensemble consistingof the choke 23 and tubes I8 and I9 is connected to the transformerauto-connected windings I2 and I3, in part by means of lead 26 extendingfrom tube I9 to lead I4, which it joins at junction 21, and in part bylead 28 extending from choke coil winding 25 to junction 29 with lead IIas shown in Figure 1.

Novelty resides in the construction of the iron choke 23. The corethereof is of generally E- shaped configuration, having an end portion30A and outer legs 30B and 300. These latter abut against one of the endpiecesIID, HE of the transformer core II, in Figure 1 shown ascomprising the end member HE. Thus the E-shaped choke core is disposedtowards the transformer I0 and abuts snugly thereagainst. The centralleg 30D of the choke core 23 extends towards, but terminates short of,the end member HE of the transformer core, so as to provide an includedair-gap 30E which tends to suppress within certain calibrated limits thecoursing f flux induced by the choke coil winding 25 within the core 30.As is evident fromconsideration of the Figure 2, the width of thetransformer and choke cores are identical so that the two elements nestsnugly against each other, in neat compass.

I have provided for effective starting and for effective and eificientand subsequent operation, however, through the provision of an ingeniousexpedient, simple in itself. That is, I insert a condenser 32 ofappreciable capacity in shunted relation across the choke 23 and itsassociated series-connected tube I8, by means of leads 33 and 34extending between junctions 29, 22. This condenser 32 is thus seen to beseries-connected by means of lead 20 with tube I9, the unit comprisingthis condenser 32 and tube I9 being in turn series-connected to thetransformer by means of leads I! and 25. Inspection will show that uponremoval of the tube I9 from its socket the entire secondary system isde-energized, while upon removal of tube I8, it is still possible forthe tube I9 to operate through the path including condenser 32, shuntingout tube I8 and choke 23- The function of the choke 23 is of course toserve as a current-limiting device for the seriesconnected tubes I 8,I9, which possess negative resistance characteristics. That is, thecharacteristics of these tubes is that once the arc is struck, theinternal resistance across the are decreases tremendously. Byconsequence, currents of large value tend to :course through the tubes.This would result in rapid destruction thereof unless current-limitingmeans are provided.

The effect of the introduction of the condenser 32 is that initially,with static conditions maintaining, the transformer potential in largemeasure is impressed across the condenser 32 and tube I9; Since at thisinstant the tubes are in their non conductive conditions and no currentflows substantially the entire transformer voltageis impressed acrossthe terminals of the tube I9. This tube: then ignites.

Immediately upon the striking of the arc in tube I9 the internalresistance of the tube falls on appreciably, so that the voltagenecessary to maintain the arc already struck likewise lowers to acomparatively small value. Accordingly, substantially all of thesecondary voltage with the exception of the small amount required tomaintain the arc in tube I9, is impressed across the terminals of thetube I8. The ensemble of choke 23 and tube [8 now displays lessresistance than does the condenser 32 because the impedance of condenser32 assumes its normal value with the flow of current supplied tube IS.The are is there fore quickly established across tube I8, once tube 59has been ignited.

The accompanying decrease in the internal resistance of tubes I3 and I9,would result in the flow of an excessive current, since the transformerIt is of the close-coupled type, except for the choke 23. It will benoted that this choke is provided in the main secondary circuit, and isseries-connected with the secondary winding I3. Therefore, it carriesthe same current as the secondary I3. For efiiciency, it is formed ofthe same wire size. Thus, an additional factor of simplicity is therebyintroduced, namely, that the choke and secondary windings are wound withthe same size wire. As a result thereof only two sizes of wire arerequired in my power unit.

The eifect of the choke is of course to induce a back magnetomotiveforce which develops a back electromotive force tending to buck the mainsecondary electromotive force, and through selfinduction, diminishingthe current flow first through the tube I9 and then, after the tube I8has struck, through tubes I8 and I9 together. To control in accuratelypredetermined manner the self-induction in the choke 23, I provide theair-gap 32E of calibrated dimensions in the leg MD.

The stack of laminations comprising central, short arm 30D of the choke23 is cross-sectional- 1y dimensioned so as to carry the maximum fluxwhich is required for proper choking action. The end-portion 30A and theouter legs- 38B and 36C have cross-sectional areas sufficient to carryapproximately one-half of the flux which courses the central leg Bill).The number of turns of winding and the current flowing therethrough,which of course is the current flowing through the main secondarywinding, determine the magnetomotive force generated in the leg D andhence is determinative, along with the air-gap 30E, of the chokingeffect of the choke 23, having given fixed cross-sectional areas of thelegs 30A- SflD inclusive, as well as selected material fro-m which thechoke laminations are formed.

It is preferred that the choke winding 25 be wound in the same directionor phase as the primary coil 12, so that as the primary flux courses tothe right in Figure 1, along central transformer leg IIA, the secondaryflux induced from the secondary winding I3, and which courses centralchoke leg 36D, will pass to the left in Figure 1, across includedair-gap 30E, and thence will split in transformer end piece HE and passupwardly anddownwardly to, and back across, outer legs 36B, 39C of theiron core choke 23. During the reverse half-cycle of current now, ofcourse, the direction of coursing of both the primary flux and the chokeflux will be in directions exactly opposite that just traced, as will bemore fully pointed out hereinafter.

It is now in order, for precise understanding of the operation of my newsystem, to trace the several circuits involved. The primary circuit fora given half-cycle will be from the left side of the source ofalternating current supply I6, as seen in the drawing, through lead I l,across junction 27, to the left side of the primary winding 62. Theprimary current then courses across pri- .mary winding I2 to the rightand thence through lead I5 back to the right side of source It. For thesucceeding half-cycle, the current flow of course will be in theopposite direction.

For the first-mentioned half-cycle of current flow in the primarywinding, the resulting secondary potential is applied across lead -23,choke winding 25, and lead 24 to tube I8. Also, it is applied throughlead 33 to condenser 32, lead 2! and tube is. Tube i9 is connected byway of lead 255, junction 2'] and lead M, to the lefthand end of theprimary winding portion E2 of the auto-transformer.

The voltage difference between leads 2% and 28. however, is notsufficient to obtain the initial ignition of the tubes I8 and I9together. Thus, open-circuit conditions maintain. Since at this pointthere is no current flow, full potential is applied by way of condenser32 to the tube I9.

As soonas the tube I9 is rendered conductive, the voltage demandthereacross reduces appreciably, due to the negative resistancecharacteristic of the tube. Only a few volts is required to maintain thearc thereacross. Moreover, as soon as the arc is struck across tube I9,a current begins to flow. Now condenser 32 interposes a substantialquadrature reactance, so that the shunt path around tube I3 and choke 23now displays high impedance to the passage current therethrough.Substantially full transformer potential is therefore impressed acrosstube I8 (since in absence of current flow in choke 23 there is novoltage drop there). The comparatively large voltage which is nowimpressed across tube I8 quickly strikes the arc thereacross, andcurrent flows through lead 28, through lead 2|, junction 22, lead 20,choke 23, lead 24 to tube I8, thence through tube I9, across which thearc has already been struck, and back through lead 28, junction 2'! andlead I4 to the left-side of the primary winding I2 of theautotransformer I2-!3.

With both tubes in conductive condition, the current flow across thesetubes would be excessive, up to the magnetic saturation values of thetransformer core II,- unless some current-limiting means such as thechoke 23 were interposed therebetween. Choke 25 admirably serves thiscurrent-limiting function, and is so calibrated as to have an impedanceunder load conditions somewhat less than that of the condenser 32, so asto insure that tube I8 is energized during operation; Moreover, winding25 of choke 23 is wound in such direction as to be in phase with that ofthe primary winding I2. Air-gap 30E is interposed between the short,central leg 30D of the E-shaped choke core and adjacent end piece HE ofthe transformer core I I, so as to limit effectively the choking actionof the member until current beginsto flow in tube I8.

. Now, with'the flow of current established, both tubes being ignited,and with the assumption that the secondary current flow is to the rightin Figure 1, current flows through lead I! away from the secondarywinding l3 to junction 29. There a small quantity of current flowsacross lead 33, condenser 32, lead 34, junction 22, lead 20, tube l9,and back through lead 26, junction 21, and lead [4 to the left-hide ofthe auto-transformer winding. The larger portion of the current,however, courses from junction 29, down lead 28, across choke winding25, lead 24, tube l8 and lead 2| to junction 22. From thence the flow isjust the same as that traced with respect to the current flowing acrossthe condenser 32. The amount of current in lamp l9 therefore somewhatexceeds that in lamp [8. This is not objectionable, however, because Ifind that greater current is required in tube I9 because of theirregular wave-form introduced by the condenser, in order to givebalanced illumination from the two tubes.

During the reverse half-cycle of secondary potential the tubes I9 and [8respectively are rendered conductive as more fully discussed above. Withboth tubes in conductive condition, the secondary current courses upfrom the left side of the auto-transformer through lead l4, to junction21, across lead 26 to tube I9 and lead 20 to junction 22. There some ofthe secondary current courses lead 34, condenser 32, lead 33, junction29, and lead I! back to the right side of the auto-transformer winding.Most of the secondary current, however, courses from junction 22, downlead 2|, across tube I8, up lead 24, through choke winding 25 and lead28, back to junction 29.

The course of the magnetic flux through choke 23, for the direction ofthe primary current flow first traced, is to the left across short leg30D of the choke core, across included air-gap 30E, to the right endportion HE of the transformer core II, where it splits into two branchstreams. While one such branch stream joins one portion of the mainmagnetic flux in core piece I IE and courses up end-piece l [B to theright side of end portion 30B and down the web portion 30A back to thecentral leg 30D,the other branch stream joins the other portion of theflux in the main core and courses down end piece I IE to the rightacross leg 30C up web 30A and to the left across central leg 30D. Duringthe next half-cycle of secondary current flow the direction of coursingof the induced flux is just the reverse of that just traced.

Since the choke Winding 25 carries the same current as the secondarywinding l3, they are wound of the same size wire. The physicaldimensions of the choke core are so selected as to be at a minimumconsistent with proper physical location of the choke winding 25. Thusthe amount of iron employed is at a minimum.

It is my desire to provide a power unit comprising the transformer,choke and condenser of minimum compass, and to correlate the outerdimensions of these three component elements so that they nest snuglyagainst each other in endto-end abutting relationship, as can be moreclosely observed from consideration of the dis closure of Figure 2. Itwill be seen that the transformer, the yoke of the choke and thecondenser have substantially the same transverse cross-section. Thethree elements are disposed in minimum compass, and provide a snug,compact and unitary construction. In overall size, my power unit,including case and compound, is somewhat more compact than the currentlyused ballast."

Consequently, it readily may replace the ballast. and its necessarystarter, in a lighting fixture.

In the practice according to my new system, the transformer 10 is mostcompact, and is rendered highly efiicient because of the direct couplingbetween the primary and secondary windings. In point of fact, I havefound in practice that the coupling is so close that in order to limitthe size and hence cost of the choke which will effectively limit thesecondary current flow, it is desirable not to position the primary andsecondary winding one on top of the other, but to dispose themside-by-side so as to permit a certain amount of leakage from theshell-type core. This provides an additional limiting factor or control,over and above that interposed by the choke and condenser.

Oscillographic study discloses that highly symmetrical and advantageouswave form is achieved. Without intending to be limited thereby, Iattribute this to the fact that the choke core is in series-connectionwith both tubes. The iron content of the transformer choke is reduced toa minimum, as has already been pointed out hereinbefore. The number ofdifferent component parts is likewise reduced to a minimum, and theseare of the simplest possible configuration. Only two sizes of copperwire are required, and the copper content itself is reduced to aminimum. Illustratively, the iron core transformer is approximatelythree by five inches in dimension, and the iron core choke iscorrespondingly small.

While it is true that the condenser 32 is somewhat larger than isordinarily used, it is not prohibitively large. Illustratively, wherethe condenser ordinarily used for power-factor regulation in afluorescent tube lighting system operating two 40 watt tubes might be inthe neighborhood of 1.85 microfarads capacity, the condenser 32 asemployed in my new assembly is of say 2.00 microfarads capacity. Goodpowerfactor thereby is had in addition to substantial freedom fromstroboscopic effect.

Since it is apparent that once the broad aspects of my invention aredisclosed, many embodiments thereof will readily suggest themselves tothose skilled in the art, I intend the foregoing to be construed asmerely illustrative, and not in a limiting sense.

I claim:

1. A fluorescent gaseous discharge tube lighting system comprising asource of alternating current electrical energy of predeterminedfrequency, an auto-transformer having a shell-type core with central legupon which primary and secondary windings are disposed in side-by-siderelation and connected together in series and with the primary windingthereof connected to said source, a pair of series-connected fluorescentgaseous discharge tubes, an iron core reactor disposed in abuttingrelation on one end of said transformer core with the winding on saidreactor connected at one end to the transformer secondary winding and atthe other end connected to one end of said series-connected fluorescenttubes, and a condenser shunted across said reactor and one only of saidtubes, said other end of said fluorescent tubes being connected to theprimary winding, and the reactor and transformer secondary winding beingformed of the same size Wire. I

2. A fluorescent gaseous discharge the lighting system comprising asource of alternating current electrical energy of predeterminedfrequency, an auto-transformer having a shell-type core with central legupon which primary and secondary windings are disposed in side-by-siderelation and connected together in series and with the primary windingthereof connected to said source, a pair of series-connected fluorescentgaseous discharge tubes, an iron core reactor of shell-type constructiondisposed in abutting relation to said transformer core with central legthereof providing an air-gap to said core and with the winding on saidreactor connected at one end to one end of the transformer secondarywinding and at the other end to said fluorescent tubes, and a condensershunted across said reactor and associated tube, said other end of saidfluorescent tubes being connected to said primary winding, the reactorwinding and primary being wound in the same direction or phase.

3. A power unit for a fluorescent tube lighting system, comprising atransformer having primary and secondary windings mounted on an ironcore and connected together in series, a choke coil having an iron coredisposed at one end of said transformer core, a condenser disposedsnugly against a free end of the unit comprised of the transformer andchoke cores, and means connecting together one end of each of saidtransformer secondary, choke coil and condenser.

4. A power unit for a fluorescent tube lighting system, comprising atransformer having a shelltype core with auto-transformer-connectedprimary and secondary windings positioned on the central leg thereof, achoke coil having an E-shaped iron core disposed at one end of saidtransformer core with the outer legs of the E-core abutting against thetransformer and the central leg extending towards but terminating shortof said transformer core to povide an included airgap, and a condenserdisposed snugly against a free end of the unit comprised of thetransformer and choke cores, one end of each of said transformer, chokeand condenser being electricallyconnected together, and with the otherends of said transformer, choke and condenser adapted to be connected tofluorescent tubes.

5. In a power unit, the combination of a transformer having a shell-typecore and primary and secondary windings disposed side-by-side inauto-transformer connection on the central leg thereof, and a choke coilhaving an E-shaped core with the outer legs directed towards andabutting against one end of said transformer core and with its centralleg extending towards but terminating short of said end to provide anair-gap, said choke coil being of the same wire size as said secondarywinding and connected in series therewith and wound in the sameelectrical direction as said primary.

J OHN HEROLD BRIDGES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,056,661 Foulke Oct. 6, 19362,301,671 Abadie Nov. 10, 1942 2,305,153 Fries Dec. 15, 1942 2,312,867Boucher Mar. 2, 1943 2,418,160 Campbell Apr. 1, 1947 2436,399 NathansonFeb. 24, 1948 2,496,981 Boucher et al. Feb. '7, 1950

